This invention relates to a fuel injector intended for use in delivering fuel under pressure to a combustion space of a compression ignition internal combustion engine. The invention relates, in particular, to an injector of the inwardly opening type in which the number of outlet openings through which fuel is injected at any instant can be controlled by controlling the position of a valve needle.
It is desirable to guide the end of the needle adjacent the outlet openings of the injector for sliding movement so that the needle remains substantially concentric with its seating when lifted from the seating. It is a first object of the present invention to provide a fuel injector of the type described hereinbefore in which the end of the needle is guided.
In order to reduce the levels of noise and particulate emissions produced by an engine it is desirable to provide an arrangement whereby the rate at which fuel is delivered to the engine can be controlled. It is also desirable to be able to adjust other injection characteristics, for example the spray pattern formed by the delivery of fuel by an injector. British Patent Application GB 2 307 007 A and European Patent Application EP 0 713 004 A both describe fuel injectors of the type in which the fuel injection characteristic can be varied, in use, by selecting different sets of fuel injector outlet openings formed in the fuel injector nozzle body. In both of these fuel injector designs, angular motion of a sleeve member, housed within the nozzle body, causes apertures formed in the sleeve to align with selected ones of the outlet openings and subsequent inward, axial motion of a valve member within the bore of the nozzle body causes fuel to be ejected from the selected outlet openings. In this way, the fuel injection characteristic can be varied, in use, by selecting different ones of the outlet openings. However, fuel injectors of this design suffer from the disadvantage that the are complex and expensive to manufacture, and have performance limitations.
British Patent Application No 9905231 describes a fuel injector including a nozzle body defining a bore within which an outwardly opening, outer valve member is slidable. Movement of the outer valve needle in an outward direction causes fuel to be ejected from an upper group of outlet openings provided in the outer valve needle. The outer valve needle defines a blind bore within which an inner valve member is slidable. Inward movement of the inner valve member causes fuel injection through a lower group of outlet openings provided in the outer valve needle. The fuel injection rate provided by the injector is controlled by means of an actuator arrangement which controls the downward force applied to the inner valve member. A disadvantage of this type of fuel injector is that, as the injector includes a valve needle of the outwardly opening type, a poor fuel spray characteristic is obtained as the outlet openings become exposed. In addition, leakage can occur from the outlet openings during undesirable stages of the fuel injection cycle.
It is a further object of the present invention to provide an alternative fuel injector which permits the fuel injection characteristic to be varied, in use, whilst alleviating at least one of the disadvantages of known fuel injectors having this capability.
According to a first aspect of the present invention there is provided a fuel injector comprising a nozzle body provided with first and second outlet openings for fuel, a valve needle slidable within a valve needle bore defined in the nozzle body, the valve needle bore being shaped to define a seating with which the valve needle is engageable to control fuel flow to a chamber, the valve needle being provided with a flow passage communicating with the chamber, movement of the valve needle away from the seating into a first fuel injecting position permitting fuel delivery through the first outlet opening and whereby movement of the valve needle away from the seating into a second fuel injecting position causes fuel in the chamber to flow through the flow passage for delivery through the second outlet opening.
The valve needle may have a surface shaped to define first and second sealing surfaces for the first and second outlet openings, whereby movement of the valve member away from the seating into the first fuel injecting position causes the first sealing surface to uncover the first outlet opening to permit fuel delivery therefrom and movement of the valve needle away from the seating into the second fuel injecting position causes the second sealing surface to uncover the second outlet opening to permit fuel delivery therefrom. The surface of the valve needle may be shaped such that the second sealing surface closes the first outlet opening in the second fuel injecting position to prevent fuel delivery therefrom. Alternatively, the valve needle may be shaped such that fuel delivery occurs through both the first and second outlet openings when the fuel injector is in the second fuel injecting position. The valve needle may be provided with a surface which is slidable over a guide surface to guide the valve needle for sliding movement within the valve needle bore.
The guide surface may be defined by a portion of the valve needle bore located downstream of the chamber. The guide surface may be defined by a guide member carried by the nozzle body.
The flow passage may be provided, at least in part, within the guide member. The flow passage may be arranged to open into an annular groove which is communicable with the second outlet opening.
The valve needle may be provided with a first annular recess communicating with the first outlet opening, whereby, in use, movement of the valve needle into the first fuel injecting position causes the chamber to communicate with the first annular recess to permit fuel delivery through the first outlet opening.
In one embodiment of the invention, the valve needle may be provided with an additional flow passage such that movement of the valve needle away from the seating into the first fuel injecting position causes fuel in the chamber to flow into the first annular recess via the flow passage and the additional flow passage to permit fuel delivery through the first outlet opening. In one embodiment of the invention, the first annular recess may be arranged such that the first and second outlet openings are closed for a period of time when the fuel injector is between the first and second fuel injecting positions.
The valve needle may also be provided with a second annular recess communicating with the second outlet opening such that movement of the valve needle into the second fuel injecting position causes fuel in the chamber to flow into the second annular recess via the flow passage to permit fuel delivery through the second outlet opening. In one embodiment of the invention, the first annular recess may be arranged to permit fuel delivery through both the first and second outlet openings at the same time.
The valve needle may be provided with an axially extending bore which defines at least part of the flow passage for fuel. The axially extending bore provided in the valve needle may be a blind bore, the open end of the axially extending bore being sealed by a sealing member.
Alternatively, the flow passage may be defined by cross drillings provided in the valve needle or by flats, slots, flutes or grooves provided on the valve needle.
In one embodiment of the invention, the valve needle may comprise an upper part provided with an upper bore and a lower part provided with a lower bore, the lower part of the valve needle being received within the upper bore. The lower bore may be a blind bore. A two-part valve needle is advantageous as the fuel injector is easy to manufacture and assemble.
The nozzle body may be shaped to define a further seating, the lower part of the valve needle including an enlarged region defining a surface which is engageable with the further seating when the valve needle is lifted to the first fuel injecting position. In use, engagement between the surface and the further seating serves to prevent the leakage of fuel from the bore in the nozzle body.
The fuel injector may further comprise a plug member received within the lower bore to reduce the volume of the flow passage available for fuel.
Control of the fuel injector may be achieved conveniently by means of an actuator arrangement for moving the valve needle between the first and second fuel injecting positions. The fuel injector only requires a single valve needle and is therefore relatively easy to manufacture and assemble.
In one embodiment of the invention, the nozzle body may comprise an upper nozzle body part provided with a through bore and a lower nozzle body part provided with a blind bore, the lower nozzle body part being received in the through bore to close an open end thereof. The seating with which the valve needle is engageable may be defined by a part of the bore provided in the lower nozzle body part.
The first and second outlet openings may conveniently be provided in the lower nozzle body part.
According to a second aspect of the present invention, there is provided a fuel injector comprising a nozzle body provided with first and second outlet openings for fuel, a valve needle slidable within a valve needle bore defined in the nozzle body, the valve needle bore being shaped to define a seating with which the valve needle is engageable to control fuel flow to a chamber, the nozzle body including an upper nozzle body part provided with a through bore and a lower nozzle body part provided with a blind bore, the lower nozzle body part being received in the through bore to close an open end thereof.